<!DOCTYPE>
<html lang="en">
<head>
  <meta http-equiv="Content-Type" content="text/html;charset=UTF-8" />
  <title>第一题不断变大的div</title>
</head>
<body>
  <div style="width: 20px;height: 20px;background: red;"></div>
</body>
</html>
<script>

var x=20;
  var T=setInterval(function(){
      var div=document.querySelector("div");
      div.style.width=x+"px";
      div.style.height=x+"px";
      x++;
      
  },100);

  


</script>